We propose, using ultrastructural and electrophysiological techniques, to study the regeneration of axons and synapses in three preparations in which we can uniquely identify the individual nerve cells. In particular, we wish to determine the cellular mechanisms responsible for the distal stump activation of severed invertebrate axons. We will also attempt to determine some mechanisms and rules responsible for the cell-to-cell specificity and/or subcellular specificity of regenerating axons and synapses. We hope to provide evidence whether misdirected, but nonfunctional, neuronal processes make contacts with other nerve cells that are ultrastructurally similar to functional contacts made on appropriate post-synaptic cells.